The present invention is directed to a branching device for optical waveguides which device decouples a component of light out of a main line formed by optical waveguides into a subsidiary line which is also formed by an optical waveguide.
Branching devices or elements of the type which will branch out a component of light from the main line into a subsidiary line are disclosed by K. Kobayashi et al, "Micro-Optics Device for Branching, Coupling, Multiplexing and Demultiplexing", 1977, International Conference of Integr., Optics and Optical Fiber Communications, B11-3, FIG. 2. In this device, a fiber F1 abuts against an end surface of a gradient lens L1 whose other end surfaces are inclined at an angle of 45.degree. to the optical axis of the gradient lens. A beam divider reflector is applied in the form of a coating to this inclined end surface. A second gradient lens L2 is arranged coaxial with the gradient lens L1 and, likewise, possesses an end surface which is inclined at an angle of 45.degree. to the optical axis and which abuts against the beam divider reflector which is in the form of a coating. A second waveguide F2 abuts against the other end surface of this gradient lens L2 which, like the corresponding end surface of the gradient lens L1, is perpendicular to the optical axis. The two waveguides F1 and F2 are arranged coaxially to the common optical axis of the two gradient lenses L1 and L2. A third gradient lens L3 is arranged adjacent the beam divider reflector and is in contact with the top surface of the gradient lens L1. The third gradient lens L3 has an optical axis which is arranged at right angles to the common optical axis of the gradient lenses L1 and L2 and intersects the beam divider reflector at an angle of 45.degree.. A third optical waveguide F3 abuts against the end surface of the gradient surface L3 which faces away from the beam divider reflector. The individual gradient lenses are dimensioned so that a group of light beams emerging from one of the optical waveguides F1, F2 or F3 are directed parallel. End beam reversal principle is used and this means that the end surface of the waveguide F1 which abuts against the gradient lens L1 is focused onto the end surface of the waveguide F2 which abuts against the gradient lens L2 and vice versa. The same applies to the gradient lens L1 and L3 in which case, however, the beam divider reflector acts as an intermediate element and is a fundamental significance.
Accordingly in the known branching devices, three gradient lenses with specific dimensions are required, although not illustrated in FIG. 2 of the above mentioned publication, the optical waveguides which are coupled to the gradient lenses are provided with halves of plug connections which are used for connecting optical waveguides to one another.
Thus, the known branching device or element is constructed from three gradient lenses which must be adjusted relative to one another during the production of the element. The following fine adjustments are also required during production:
1. adjustment of the waveguide F2 to the gradient lens L2; PA1 2. adjustment of the waveguide F3 to the gradient lens L3. It should be pointed out that the adjustment of the waveguide F1 to the gradient lens L1 is not required as it is provided by the first two adjustments if the lens elements were already connected to one another; PA1 3. adjustment of one plug half to waveguide F1; PA1 4. adjustment of one plug half to the waveguide F2; and PA1 5. adjustment of one plug half to waveguide F3.
Thus, a total of five optical fine adjustments must be carried out.